You have only one proper way - to write your own indicator where you get values of both these indicators RSI and MACD (for example) and you have to invent the way to check condition which you need.
When this condition is triggered you need to draw a raw to buy or to sell. Also, you can obtain such triggerings as values in another indicator or EA.
Is there a way using Win API to determine what the top and bottom value of the window are (i.e. the scale). Or could you provide some insight on which api is implemented and how?
Even if you place 2 ATR with different Periods in the same sub-window the crossing that you see might correspond to a crossing in the data or not - that's mt4 :(
The only thing you can do is write you own indicator..
It do not seem difficult to turn a MACD into a percent MACD, but one's have to determine what will match with the 0% and the 100% .
Either someone on a forum was saying that overlaying an RSI with an ATR would give good crossing point, but what would be the 0% and the 100% for the ATR ?